I am playing with Ansca "Fishies" example and added a ball to hit the fishes, Also add fishes to physics and added eventlisttener for colission detection as below:
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fishOriginal[i] = display.newImage(file1)
physics.addBody(fishOriginal[i],BirdsBodyElement)
fishOriginal[i].name="Red one"..tostring(i)
group:insert( fishOriginal[i], true ) -- accessed in buttonListener as group[1]

Runtime:addEventListener( "collision", onCollision )
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But strange thing is that : if fishes are on the LEFT side of the screen, when fishes are hited with ball, collision is detected. but if fishes on RIGHT side of the screen, the colission could not be detected.

Can anybody help and give me a clue.

Thanks in advance